Re-entrancy guard for length tuner tool.

Fixes https://gitlab.com/kicad/code/kicad/-/issues/15268

pcbnew/router/length_tuner_tool.cpp

@@ -278,6 +278,11 @@ void LENGTH_TUNER_TOOL::setTransitions()
 
 int LENGTH_TUNER_TOOL::MainLoop( const TOOL_EVENT& aEvent )
 {
+    if( m_inLengthTuner )
+        return 0;
+
+    REENTRANCY_GUARD guard( &m_inLengthTuner );
+
     // Deselect all items
     m_toolMgr->RunAction( PCB_ACTIONS::selectionClear );
 

pcbnew/router/length_tuner_tool.h

@@ -51,6 +51,7 @@ private:
 
     PNS::MEANDER_SETTINGS m_savedMeanderSettings;
     PNS::ROUTER_MODE      m_lastTuneMode;
+    bool                  m_inLengthTuner;
 };
 
 #endif